1. Field of the Invention
The present invention relates to a magnetic recording medium and a method of forming the same and a magnetic disk drive and, more particularly, a magnetic recording medium having magnetic patterns into which servo information (track position information) are written and a magnetic recording layer into which data are written and a method of forming the same and a magnetic disk drive which is equipped with the magnetic recording medium.
2. Description of the Prior Art
In order to enhance a magnetic recording density, there is a tendency to increase a track density of the magnetic recording medium (magnetic disk) in the field of the magnetic disk drive. Improvements in tracking accuracy of the magnetic head are indispensable for accomplishing the high track density. Various tracking servomechanisms such as servo surface servomechanism, sector servomechanism, buried servomechanism, or the like may be considered as a means for detecting the tracking position.
In these servomechanisms, servo signals written into the magnetic disk are read by means of the magnetic head, and a head actuator is controlled based on the servo signals to shift the magnetic head to a target track position.
As the magnetic recording medium having a structure for recording both the servo signals and data information, as set forth in Japanese Patent Application Publication (KOKAI) 2-218016, for instance, there has been proposed such a method that uneven bits to be read magnetically are provided on the surface of the magnetic recording medium, then magnetic fluxes generated from ends of the bits are detected as tracking signals, and then position of the magnetic head is controlled based on the tracking signals. The structure with the magnetic recording layer on the bits and the structure without the magnetic recording layer on the bits have been proposed.
However, the presence of the uneven surface of the magnetic recording medium prevents the magnetic head from being in a lower flying height state over the magnetic disk. Such uneven surface causes trouble if a high recording density should be achieved by decreasing the flying height of the magnetic head. Moreover, if the magnetic disk has an uneven surface, dusts are easily accumulated in concave portions on the uneven surface of the magnetic recording medium.
On the other hand, in Japanese Patent Application Publications (KOKAIs) 59-72644 and 4-34718, there has been set forth that a magnetic recording medium having the structure wherein magnetic substance patterns (referred to as "servo patterns" hereinafter) for recording servo information therein are formed on the substrate, and then the nonmagnetic layer and the magnetic recording layer are formed on the servo patterns and the substrate in sequence.
In Japanese Patent Application Publication (KOKAI) 4-34718, there has been set forth that the servo patterns are to be formed by a lift-off method, thereby improving surface evenness of the magnetic recording layer.
However, according to the structures of the servo patterns set forth in these publications (KOKAIs), the servo patterns and the magnetic head are positioned at a good distance away since not only a gap due to the flying height of the magnetic head but also the nonmagnetic layer and the magnetic recording layer are present between the servo patterns and the magnetic head. For this reason, read error of the servo signals easily occurs because, with the longer distance between the servo patterns and the magnetic head, the signal magnetic fields generated from the servo patterns to the magnetic head is lessened.
If the lift-off method is utilized to form the servo patterns, flashes are prone to be formed around peripheries of the servo patterns. The occurrence of flashes increases the likelihood of a head crash of the magnetic head in the low flying height region. In order to achieve high track density, the precision of tracking the magnetic head has to be improved. For example, the phase servo system has been used to detect information with regard to the tracking position.
The phase servo system is that the servo patterns are arranged to change the phase of the reproduced servo signal according to position of the magnetic head in the track direction (circumferential direction).
In the prior art, in order to record such servo patterns on the surface of the magnetic recording medium, a following method has been employed. For instance, as shown in FIG. 1A, while the magnetic head 120 is being shifted in the width direction of the track 110 by the first pitch L1 having a length which can be divided into plural lengths (e.g., three to four lengths) in the width direction (diameter direction) of the track 110 and concurrently the magnetic head 120 is being shifted by the second pitch L2 in the circumferential direction, a plurality of magnetization inversion patterns are formed on the surface of the magnetic recording medium. The magnetization inversion patterns are utilized as the servo patterns 130. A width of magnetic pole of a recording inductive head of the magnetic head 120 is almost identical to the track width.
The precision of detecting the tracking (track alignment) information in the phase servo system becomes higher as the number of split Dervo patterns formed in each track in the diameter direction increases. Such precision also becomes higher as the servo patterns 130 are made more sharply.
However, the higher the number of split Dervo patterns in each track 110, the higher the recording time of the servo patterns 110 per one sheet of the magnetic recording medium. Further, if the number of splits Dervo patterns in each track 110 is increased, the alignment precision of the magnetic head 120 is reduced in the high density track upon recording the servo patterns 130. Still further, as shown in FIG. 1B, because of leakage magnetic field generated from end portions of the magnetic pole of the magnetic head 120, bit bends 131 occur at the end of the servo pattern 130. Otherwise, because of recording bleeding, erase regions 132 occur at the end of the servo pattern 130. As a result, there is such a problem that the quality of servo information is debased.
Since small servo patterns per bit, as set forth in Patent Application Publication (KOKAI) 59-72644, are formed in plural numbers within one track, omissions of such patterns would be caused upon etching to form the servo patterns.